Duct fastseam

ABSTRACT

A seam for ductwork has a male end portion integrally formed at a distal end of a duct wall and a female end portion integrally formed at another distal end of the duct wall. The female end portion includes a first fold and a second fold, which define a female groove for accommodating the male portion. A distal end of the second fold is bent transverse to the female groove prior to the male portion being inserted into the female groove.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional application of U.S. Utility applicationSer. No. 10/668,734, filed on Sep. 23, 2003, and claims the benefit ofU.S. Provisional Application Ser. No. 60/412,740, filed on Sep. 23,2002, both of which are herein incorporated by reference in theirentireties.

FIELD OF THE INVENTION

This invention relates in general to a duct fastseam, and deals moreparticularly with a duct fastseam, which may be easily assembled byhand.

BACKGROUND OF THE INVENTION

Rectangular or box-shaped ducts are extensively utilized in heating andventilating systems to distribute heated or cooled air throughout astructure. These ducts are commonly formed from differing gauges ofsheet metal in sections of predetermined lengths, which are thenconnected to one another to form a continuous duct for distributing air.

Typically, each section of duct is formed by bending two pieces of sheetmetal of the desired length at a 90° angle. One edge of each piece isformed to include a longitudinally extending groove, forming thereby thefemale portion of the seam, while the other longitudinal edge of eachpiece is bent over along its length to form thereby the male portion ofthe seam. The two pieces are then assembled by inserting the maleportion of each piece into the female portion, leaving an edge extendingbeyond the joint from the female portion. This extended edge must thenbe bent over to lock the seam. This seam is known in the industry as a‘Pittsburgh’ lock or seam.

While these known duct systems are successful to a degree, they sufferfrom several logistical problems. Firstly, the insertion of the maleportion into the female portion of the seam requires a great deal offorce due to the tight dimensional constraints of the formed female end.To accomplish this goal, operators must force the male end into thefemale end, typically utilizing a hammer or the like. Likewise, theextended edge of the female portion must also be hammered over in orderto lock the seam closed. These hammering operations are highly laborintensive and quite loud, oftentimes requiring ear protection for theoperators who assemble the finished duct work. Moreover, the time andeffort extended on hammering the male portion into the female portion,and then hammering the extended edge of the female portion over to sealthe seam, can substantially increase the time and expense of any ductfabrication and installation job, typically by as much as 50% or more.

With the forgoing problems and concerns in mind, it is the generalobject of the present invention to provide a duct fastseam, whichovercomes the above-described drawbacks while maximizing effectivenessand flexibility in the assembling process.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a duct fastseam.

It is another object of the present invention to provide a duct fastseamthat may significantly reduce the assembly time of ductwork.

It is another object of the present invention to provide a duct fastseamwhich may significantly reduce the noise associated with assembling ductwork.

It is another object of the present invention to provide a duct fastseamthat may be fitted together manually, without tooling.

It is another object of the present invention to provide a duct fastseamthat may be easily fitted together by hand.

It is another object of the present invention to provide a duct fastseamthat is capable of maintaining the duct in a substantially squarecondition even when the fastseam has yet to be completely sealed.

It is another object of the present invention to provide a duct fastseamthat may be completely sealed by a sealing apparatus employing only asingle roller.

It is another object of the present invention to provide a duct fastseamthat resembles a known Pittsburgh seam when completely sealed.

These and other objectives of the present invention, and their preferredembodiments, shall become clear by consideration of the specification,claims and drawings taken as a whole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a known duct seam.

FIG. 2 is a cross-sectional view of the female end of a duct fastseam,according to a first embodiment of the present invention.

FIG. 3 is a cross-sectional view of the male end of the duct fastseam asit is being inserted into the female end illustrated in FIG. 2.

FIG. 4 is a cross-sectional view of the male end of the duct fastseamafter it is inserted into the female end illustrated in FIG. 2.

FIG. 5 is a cross-sectional view of the female end of a duct fastseam,according to another embodiment of the present invention.

FIG. 6 is a cross-sectional view of the male end of a duct fastseam asit is being inserted into the female end illustrated in FIG. 5.

FIG. 7 is a cross-sectional view of the male end of the duct seam afterit is inserted into the female end illustrated in FIG. 5.

FIG. 8 is a cross-sectional view of the male end of a duct fastseam asit is being inserted into the female end, according to anotherembodiment of the present invention.

FIG. 9 is a cross-sectional view of the male end of the duct seam afterit is inserted into the female end illustrated of FIG. 8.

FIG. 10 is a cross-sectional view of the male end of the duct seam afterit is inserted into the female end of the duct seam, according toanother embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a cross-sectional view of know duct seam 10, commonlyreferred to in the field as a ‘Pittsburgh’ seam. As shown in FIG. 1, theseam 10 includes a female portion 12 which is formed by repetitivelybending, or roll forming, the duct material, typically sheet metal orthe like, so as to form three substantially parallel folds 14. The folds14 serve to define a female groove 16, wherein one of the folds 14preliminarily extends beyond the duct edge to establish a sealingportion 18.

The seam 10 further includes a longitudinal section of the duct wall 20,which is bent at a substantially right angle to form a male portion 22.As will be appreciated, the male portion 22 is sized for tight fittingwithin the female groove 16 of the female portion 12 when fullyassembled.

In operation, the male portion 22 of the seam 10 is initially fittedinto the female groove 16 when the sealing portion 18 remains in itsunsealed position, as represented by the dashed lines in FIG. 1.

Once the male portion 22 has been inserted into the female groove 16,the sealing portion 18 must then be hammered or otherwise bent down, inthe direction of the arrow A, against the duct wall 20 in order tocomplete the sealing of the seam 10. The hammering over of the sealingportion 18 is typically accomplished either manually, or with the use ofa pneumatic hammer or the like. It will be readily appreciated that thehammering of the male portion 22 and the sealing portion 18 is highlytime consuming and oftentimes noisy to the point of being injurious tothe ears of the operators who are assembling the seam 10. It shouldadditionally be noted that prior to the sealing portion 18 beinghammered-over to complete the sealing process, the seam 10 is incapableof maintaining a substantially square condition. That is, without beingcompletely sealed, the male portion 22 of the seam 10 will disengagefrom the female groove 16 and cause thereby the seam 10 to lose itsstructural form.

In contrast, FIG. 2 illustrates one half of a fastseam 100 which iscapable of maintaining its structural form, even when the sealingprocess is not yet completed, according to one embodiment of the presentinvention. As depicted in FIG. 2, the fastseam 100 includes a femaleportion 102 that is formed by longitudinally bending, or roll forming, aplane of duct material so as to form a hemmed ridge 104 and a femalegroove 106.

The duct wall 108 is initially bent inwards, that is, towards what willeventually become the interior 109 (as shown in FIG. 4) of the finishedduct, to form the first fold 110 of the hemmed ridge 104. The first fold110 is then bent back upon itself in a non-parallel manner to form asecond fold 112 of the hemmed ridge 104. The plane of the second fold112 is then broken in the area adjacent the break point 114 of the firstfold 110, to form a third fold 116 which extends a predetermineddistance substantially parallel to, and in close association with, theplane of the duct wall 108.

The third fold 116 is bent outwards, that is, away from the duct wall108, and back upon itself to form a fourth fold 118 extendingsubstantially parallel to the duct wall 108. As depicted in FIG. 2, thefemale groove 106 defined between the third fold 116 and the fourth fold118 is dimensioned to be slightly larger than the thickness of the ductmaterial utilized in the formation of a male portion of the fastseam100, as will be described in more detail later.

The fourth fold 118 includes a sealing portion 120, which is benttransverse to the female groove 106 prior to an unillustrated maleportion being inserted into the female groove 106. The sealing portion120 may then be further bent in the direction of arrow B in order tocompletely seal the fastseam 100 when the unillustrated male portion isinserted into the female groove 106.

Turning to FIG. 3, the fastseam 100 further includes a longitudinalsection of a matching duct wall 122 which is bent at a substantiallyright angle to form a male portion 124. The male portion 124 may then beinserted into the female groove 106 of the female portion 102 in thegeneral direction of arrow C. The male portion 124 is the equivalent ofthe male portion 22 discussed in conjunction with FIG. 1.

It is therefore an important aspect of the present invention that thehemmed ridge 104 and the sealing portion 120 are formed at the properangles in order to permit the insertion of the male portion 124 into thefemale groove 106 without the use of a hammer or the like. That is,during assembly, the walls of the rectangular duct are slightlydeformed, with respect to one another, from a square condition to aparallelogram condition to allow the male portion 124 to be eased intothe female groove 106 without the use of any tools. Moreover, incontrast with the commonly known Pittsburgh seam illustrated in FIG. 1,the angles at which the hemmed ridge 104 and the sealing portion 120 areformed, effectively prevent the male portion 124 from disengaging fromthe female groove 106 once the two have been fitted together.

It is envisioned that the hemmed angle α is formed preferable between 10to 60 degrees, and more preferably is formed at approximately 30degrees. Moreover, the sealing angle β is envisioned to be formed mostpreferably between 45 and 60 degrees. It will be readily appreciatedthat hemmed angle α and sealing angle β work in conjunction with oneanother to permit enough clearance in the female portion 102 to allowthe male portion 124 to be position in the female groove 106 with aminimum amount of applied force, while also preventing the male portion124 from disengaging from the female groove 106 after being positionedtherein.

It will further be appreciated that the relationship between the hemmedangle α and sealing angle β is such that they are generally inverselyproportional to one another, wherein when, for example, the hemmed angleα is increased, the sealing angle β may be correspondingly decreased.Regardless of the specific angles utilized by the hemmed angle α andsealing angle β, the primary consideration is to ensure enoughdimensional clearance to permit the male portion 124 to be inserted intothe female groove 106 without the use of hammers or other tools, aspreviously mentioned.

It should also be noted that another important consideration does exist,however, regarding the magnitude of the sealing angle β. As has beendiscussed previously, the sealing portion 120 must be bent over in orderto finish the sealing process of the fastseam 100. Towards this end, itwill be readily apparent that the larger the sealing angle β is, theeasier it will be to bend the sealing portion 120 to its sealedposition. Likewise, the smaller the sealing angle β is, the more effortwill be required to bend the sealing portion 120 to its sealed position.

It is therefore another important aspect of the present invention thatthe fastseam 100 includes a partially ‘hammered-over’ sealing portion120. That is, by forming the female portion 102 to include a sealingportion 120 which is inclined at the sealing angle β, the presentinvention makes the subsequent sealing process of the ductwork mucheasier, quieter and less labor intensive, even if tradition hammering islater employed for this purpose. The present invention, however,effectively removes the necessity for any hammering, manual orpneumatic, to complete the sealing process and instead enables the useof a single-roller sealing apparatus to be employed for this purpose.

FIG. 4 illustrates the condition of the fastseam 100 after the maleportion 124 has been hand-inserted into the female groove 106. As shownin FIG. 4, it is another important aspect of the present invention thatonce the male portion 124 is located in the female groove 106 and thewalls of the rectangular duct 111 are relaxed with respect to oneanother, back to their original square condition, that the configurationof the fastseam 100 prevents the disengagement of the male portion 124,even when the sealing portion 120 has not yet been completely bent overto complete the sealing process.

For the purposes of this invention, a ‘square condition’ refers to thecondition in which there exists a substantially perpendicularrelationship between the duct wall 122 and the duct wall 126. Likewise,a ‘parallelogram condition’ refers to the condition in which the ductwall 122 and the duct wall 126 have been forced, temporarily, into anorientation in which there does not exist a substantially perpendicularrelationship between the duct wall 122 and the duct wall 126, as shownin FIG. 3.

Returning to FIG. 4, the ability of the fastseam 100 to prevent thedisengagement of the male portion 124 from the female groove 106, oncethe fastseam is relaxed into its square condition, provides manyinherent advantages. Not only can the fastseam 100 be initiallyassembled by hand, without the use of hammers or the like, but onceassembled, the fastseam 100 maintains its structural integrity until itcan be completely sealed by bending the sealing portion 120 in thegeneral direction of arrow D via a single roller sealing apparatus, asdiscussed previously. Moreover, the present invention provides a lesscumbersome and more streamlined assembly process on the whole,especially as the partially assembled ducts may be easily handledwithout coming apart despite not being completely sealed.

FIG. 5 illustrates one half of a fastseam 200, which also does notrequire the use of a hammer or the like during its initial assembly,according to another embodiment of the present invention. As depicted inFIG. 5, the fastseam 200 includes a female portion 202 which is formedby repetitively bending, or roll forming, the duct material, typicallysheet metal or the like, back upon itself so as to form an open fold204. The open fold 204, in association with a substantially parallelfold 208, serves to define a female groove 206, wherein the open fold204 includes a sealing portion/fold 220 bent at an angle to the openfold 204 prior to a male portion of the fastseam being inserted into thefemale groove 206. The sealing portion 206 may then be bent in thedirection of arrow E in order to completely seal the fastseam 200 afterthe unillustrated male portion is inserted into the female groove 206.

It will be readily appreciated that by forming the sealing portion/fold220 to be bent at an angle to the open fold 204 prior to a male portionof the fastseam being inserted into the female groove 206, in contrastto the configuration of known Pittsburgh seams, the present inventionensures that the male portion of the fastseam may remain partiallysecured within the female groove 206 even prior to the sealingportion/fold 220 being completely sealed by a roller or the like.

As depicted in FIG. 5, the female groove 206 defined between the openfold 204 and the parallel fold 208 is dimensioned to be slightly largerthan the thickness of the duct material utilized in the formation of amale portion of the fastseam 200, as will be described in more detaillater.

Turning to FIG. 6, the fastseam 200 further includes a longitudinalsection of a matching duct wall 222 which is bent at a substantiallyright angle to form a male portion 224. The male portion 224 may then beinserted into the female groove 206 of the female portion 202 in thegeneral direction of arrow E.

It is therefore an important aspect of the present invention that,similar to the embodiment disclosed in FIGS. 2-4, the open fold 204 andthe sealing portion 220 are formed at the proper angles in order topermit the insertion of the male portion 224 into the female groove 206without the use of a hammer or the like. That is, during assembly, thewalls of the rectangular duct are slightly deformed, with respect to oneanother, from a square condition to a parallelogram condition to allowthe male portion 224 to be eased into the female groove 206 without theuse of any tools.

It is envisioned that the open angle φ be formed preferable between 10to 30 degrees, and more preferably to be formed at approximately 20degrees from the parallel plane defined by the parallel fold 208.Moreover, the sealing angle ω is envisioned to be formed most preferablybetween 45 and 60 degrees. It will be readily appreciated that the openangle φ and sealing angle ω work in conjunction with one another topermit enough clearance in the female portion 202 to allow the maleportion 224 to be position in the female groove 206 with a minimumamount of applied force.

It will further be appreciated that the relationship between the openangle φ and sealing angle ω is such that they are generally proportionalto one another, wherein when, for example, the open angle φ isincreased, the sealing angle ω may also be correspondingly increased.Regardless of the specific angles utilized by the open angle φ andsealing angle ω, the primary consideration is to ensure enoughdimensional clearance to permit the male portion 224 to be inserted intothe female groove 206 without the use of hammers or other tools, aspreviously mentioned.

It should also be noted that another important consideration does exist,however, regarding the magnitude of the sealing angle ω. As has beendiscussed previously, the sealing portion 220 must be bent over in orderto finish the sealing process of the fastseam 200. Towards this end, itwill be readily apparent that the larger the sealing angle ω is, theeasier it will be to bend the sealing portion 220 to its sealedposition. Likewise, the smaller the sealing angle ω is, the more effortwill be required to bend the sealing portion 220 to its sealed position.By forming the female portion 202 to include a sealing portion 220 whichis already inclined at the sealing angle ω, another important aspect ofthe present invention is also realized. That is, the sealing portion 220makes the subsequent sealing process of the ductwork much easier,quieter and less labor intensive, even if tradition hammering is lateremployed for this purpose.

As mentioned previously in conjunction with the embodiment illustratedin FIGS. 2-4, the inclined orientation of the sealing portion 220effectively removes the necessity for any hammering, manual orpneumatic, to complete the sealing process of the fastseam 200 andinstead enables the use of a single-roller sealing apparatus to beemployed for this purpose.

FIG. 7 illustrates the condition of the fastseam 200 after the maleportion 224 has been hand-inserted into the female groove 206. As shownin FIG. 7, it is another important aspect of the present invention thatonce the male portion 224 is located in the female groove 206 and thewalls of the rectangular duct are relaxed, with respect to one another,back to their original square condition, that the configuration of thefastseam 200 prevents the disengagement of the male portion 224, evenwhen the sealing portion 220 has not yet been bent over to complete thesealing process.

As discussed previously, the ability of the fastseam 200 to prevent thedisengagement of the male portion 224 from the female groove 206, oncethe fastseam is relaxed into its square condition, provides manyinherent advantages. Not only can the fastseam 200 be initiallyassembled by hand, without the use of hammers or the like, but onceassembled, the fastseam 200 maintains its structural integrity until itcan be completely sealed by bending the sealing portion 220 in thegeneral direction of arrow G via a single roller sealing apparatus, asdiscussed previously. Moreover, the present invention provides a lesscumbersome and more streamlined assembly process on the whole,especially as the partially assembled duct may be easily handled withoutcoming apart despite not being completely sealed, similar to theembodiment discussed in conjunction with FIGS. 2-4.

FIGS. 8 and 9 illustrate yet another embodiment of the presentinvention. As depicted in FIG. 8, the fastseam 300 includes a femaleportion 302 that is formed by longitudinally bending, or roll forming, aplane of duct material so as to form a hemmed ridge 304 and a femalegroove 306.

The duct wall 308 is initially bent inwards, that is, towards what willeventually become the interior of the finished duct, to form the firstfold 310 of the hemmed ridge 304. The first fold 310 is then bent backupon itself in a parallel manner to form a second fold 312 of the hemmedridge 304. The hemmed ridge 304 is therefore inwardly formed to besubstantially perpendicular to the duct wall 308. The second fold 112continues until it is broken at a break point 313 which liesapproximately in the plane defining the exterior wall of the duct wall308. A third fold 316 extends a predetermined distance from the breakpoint 313 at an open angle γ, as measured from the plane defining theexterior wall of the duct wall 308.

The third fold 316 is itself bent inwards at a sealing angle λ to form afourth fold 318, ending in a substantially perpendicularly formedsealing portion 320. The sealing portion 320 will be bent in thedirection of arrow I in order to seal the fastseam 300 when the maleportion 324 has been inserted into the female groove 306 in the generaldirection of arrow H.

It is therefore an important aspect of the present invention that,similar to the embodiments disclosed in FIGS. 2-7, the open angle γ andthe sealing angle λ are formed so as to permit the insertion of the maleportion 324 into the female groove 306 without the use of a hammer orthe like. That is, during assembly, the walls of the rectangular ductare slightly deformed, with respect to one another, from a squarecondition to a parallelogram condition to allow the male portion 324 tobe eased into the female groove 306 without the use of any tools.

It is envisioned that the open angle γ is formed preferable between 5 to45 degrees, and more preferably is formed at approximately 20 degreesfrom the plane defining the exterior of the duct wall 308. Moreover, thesealing angle λ is envisioned to be formed most preferably between 30and 60 degrees, and more preferably is formed at approximately 45degrees. It will be readily appreciated that the open angle γ andsealing angle λ work in conjunction with one another to permit enoughclearance in the female portion 302 to allow the male portion 324 to beposition in the female groove 306 with a minimum amount of appliedforce.

It will further be appreciated that the relationship between the openangle γ and sealing angle λ is such that they are generally inverselyproportional to one another, wherein when, for example, the open angle γis increased, the sealing angle λ may also be correspondingly decreased.Regardless of the specific angles utilized by the open angle γ andsealing angle λ, the primary consideration is to ensure enoughdimensional clearance to permit the male portion 324 to be inserted intothe female groove 306 without the use of hammers or other tools, aspreviously mentioned.

It is another important aspect of the present invention that once themale portion 324 is located in the female groove 306 and the walls ofthe rectangular duct are relaxed, with respect to one another, back totheir original square condition, that the configuration of the fastseam300 prevents the disengagement of the male portion 324, even when thesealing portion 320 has not yet been bent over to complete the sealingprocess.

As discussed previously, the ability of the fastseam 300 to prevent thedisengagement of the male portion 324 from the female groove 306, oncethe fastseam is relaxed into its square condition, provides manyinherent advantages. Not only can the fastseam 300 be initiallyassembled by hand, without the use of hammers or the like, but onceassembled, the fastseam 300 maintains its structural integrity until itcan be completely sealed by bending the sealing portion 320 in thegeneral direction of arrow H via a single roller sealing apparatus, asdiscussed previously. Moreover, the present invention provides a lesscumbersome and more streamlined assembly process on the whole,especially as the partially assembled duct may be easily handled withoutcoming apart despite not being completely sealed, similar to theembodiment discussed in conjunction with FIGS. 2-7.

It should also be noted that another important consideration does exist,however, regarding the magnitude of the sealing angle λ. As has beendiscussed previously, the sealing portion 320 must be bent over in orderto finish the sealing process of the fastseam 300. Towards this end, itwill be readily apparent that the smaller the sealing angle λ is, theeasier it will be to bend the sealing portion 320 to its sealedposition. Likewise, the larger the sealing angle λ is, the more effortwill be required to bend the sealing portion 320 to its sealed position.

As mentioned previously in conjunction with the embodiment illustratedin FIGS. 2-7, the inclined orientation of the sealing portion 320effectively removes the necessity for any hammering, manual orpneumatic, to complete the sealing process of the fastseam 300 andinstead enables the use of a single-roller sealing apparatus to beemployed for this purpose.

FIG. 9 illustrates the condition of the fastseam 300 after the maleportion 324 has been hand-inserted into the female groove 306 and thesealing portion 320 has been bent over to complete the sealing process.

FIG. 10 illustrates the condition of a fastseam 400 according to yetanother embodiment of the present invention. As shown in FIG. 10, thefastseam 400 includes a first fold 402 bent to extend inwardly andsubstantially perpendicular to the duct wall 404, a second fold 406 bentto extend in a direction substantially parallel to said duct wall 404, athird fold 408 bent back upon the second fold 406, and a fourth fold 410bent at an open angle π from the third fold 408 and defining thereby afemale groove 412 for accommodating a male portion 414 therein.

As is also seen in FIG. 10, a sealing portion 416 is bent transverse tothe female groove 412 prior to the male portion 414 being inserted intothe female groove 412. Moreover, according to a preferred embodiment ofthe present invention, the open angle π is preferably between 10 to 60degrees.

As will be appreciated by consideration of the embodiments illustratedin FIGS. 2-10, the present invention provides a fastseam for ductshaving a heretofore unknown ease and flexibility of assembly. Moreover,the fastseam of the present invention also advantageously promotes aquicker initial assembly of the ductwork without requiring that thefastseam be completely sealed in order to maintain the substantiallysquare condition of the ductwork. Another inherent benefit of thepresent invention resides in the ability of the fastseam to closely andsubstantially resemble the configuration of a completely sealedPittsburgh seam, an industry standard. The further ability of thepresent invention to be sealed by a single roller sealing apparatus,rather than requiring labor intensive and loud hammering, is also ofsubstantial benefit as compared to prior art seams.

While the invention has been described with reference to the preferredembodiments, it will be understood by those skilled in the art thatvarious obvious changes may be made, and equivalents may be substitutedfor elements thereof, without departing from the essential scope of thepresent invention. Therefore, it is intended that the invention not belimited to the particular embodiments disclosed, but that the inventionincludes all equivalent embodiments.

1. A seam for ductwork, said seam having a male end portion integrallyformed with said ductwork, said seam comprising: a female end portionintegrally formed with said ductwork; wherein said female end portionincludes a first fold and a second fold, said first and second foldsdefining thereby a female groove for accommodating said male end portiontherein; wherein a distal end of said second fold is bent away from saidfemale groove prior to said male end portion being inserted into saidfemale groove; and wherein said female groove lies adjacent an outersurface of said ductwork.
 2. The seam for ductwork according to claim 1,wherein: said first fold extends from an inwardly formed hemmed ridge,said inwardly formed hemmed ridge being substantially perpendicular tosaid duct wall.
 3. The seam for ductwork according to claim 1, wherein:said first fold and said second fold define a sealing angle ofapproximately 5 to 45 degrees therebetween.
 4. The seam for ductworkaccording to claim 1, wherein: said first fold and said second folddefine a sealing angle of approximately 20 degrees therebetween.
 5. Aseam for ductwork having a male end portion integrally formed at adistal end of a duct wall, said seam comprising: a female end portionintegrally formed at another distal end of said duct wall; and whereinsaid female end portion includes a first fold which is bent to extend ina first direction substantially parallel to said duct wall, a secondfold which is bent at an open angle and extends in a second direction todefine a female groove for accommodating said male end portion therein,and a sealing fold integrally formed at a distal end of said secondfold, said sealing fold being bent at a sealing angle to said secondfold prior to said male portion being inserted into said female groove.6. The seam for ductwork according to claim 5, wherein: said seconddirection is substantially opposite to said first direction.
 7. The seamfor ductwork according to claim 5, wherein: said open angle is between10 to 30 degrees.
 8. The seam for ductwork according to claim 5,wherein: said open angle is approximately 20 degrees.
 9. The seam forductwork according to claim 5, wherein: said sealing fold is benttowards said duct wall.
 10. The seam for ductwork according to claim 5,wherein: said sealing angle is between 45 to 60 degrees.
 11. A seam forductwork having a male end portion integrally formed at a distal end ofa duct wall, said seam comprising: a female end portion integrallyformed at another distal end of said duct wall; and wherein said femaleend portion includes a first fold bent to extend inwardly andsubstantially perpendicular to said duct wall, a second fold bent toextend in a direction substantially parallel to said duct wall, a thirdfold bent back upon said second fold, and a fourth fold bent at an openangle from said third fold and defining thereby a female groove foraccommodating said male portion therein.
 12. The seam for ductworkaccording to claim 11, further comprising: a distal end of said fourthfold bent transverse to said female groove prior to said male portionbeing inserted into said female groove.
 13. The seam for ductworkaccording to claim 12, wherein: said open angle is between 10 to 60degrees.